Minecraft model / texture not loading, what to do?

I've been trying to play around with Texture Pack's for a while (yes, also 3D textures)

and at some point it happens that as soon as I open a texture pack in minecraft that the model and the texture of the horse are no longer displayed (yes only from the horse). The only thing you see is a beautiful shade, what have I done? Or how can I change that again?

Horse textures in the entity folder have already been deleted / added etc. Did nothing.
Yes, 3D model was also deleted (from the texture pack).
If I don't have a texture pack in it, everything is ok, but as soon as I put it in, no matter what, the model is no longer available.
Oh and maybe important: when I hit the horse my screen turns red permanently.

Did you accidentally do something in the Minecraft gamefiles?